Biomedical subjects

Yasuyuki Takahashi

Publications and source records attributed to Yasuyuki Takahashi.

8 recordsLinked to original sources

PubMed2005

[Present status and issues regarding X-ray medical checkup vehicles in preventive medicine: usefulness of mass screening for lung cancer by an X-ray medical checkup vehicle].

Although the prevention of habituation-related diseases has become an important topic in Japan, the early detection of cancers such as lung, gastric, and breast cancers is an important issue for X-ray-related imaging modalities. High cost-benefit and cost-effectiveness are necessary to perform mass screenings such as those for lung cancer. In order to assess cost-benefit and cost-effectiveness, a total of 100 institutions nationwide were investigated, with a 41% of recovery rate. There were at least one or two institutions in each prefecture. Cost-benefit analysis was based on factors including the price of the medical check-up vehicle, its service life, and income from the examinations. The mean price of medical check-up vehicles used for chest X-ray examinations was 4,445,000 yen. Cost-effectiveness analysis was based on the expense incurred to discover one lung cancer. According to our research, the cost-effectiveness involved in detecting one lung cancer by conventional chest X-ray examination was about 2,270,167 yen/person. Since this amount seems unduly high, it is necessary to improve cost-effectiveness.

Cost-Benefit Analysis↗

PubMed2005

The effects of epinephrine in local anesthetics on plasma catecholamine and hemodynamic responses.

In order to clarify the influence of epinephrine in local anesthetics on endogenous epinephrine, we examined the concentration of plasma catecholamines (epinephrine and norepinephrine) and hemodynamics by administering 4 ml of 2% lidocaine containing different concentrations of epinephrine. Forty-three healthy adult male volunteers were divided into five groups according to epinephrine concentration: 0-microg (group I), 10-microg (group II), 20-microg (group III), 40-microg (group IV), and 50-microg (group V). The parameters were examined immediately, and at 1, 2, 3, 4, 5, 10, 15, and 20 min after the injection. In groups II, III, IV, and V, the plasma epinephrine concentration was elevated to peak at 5 min after the injection, after which it started to decline. The amount of increase in the plasma epinephrine concentration at 5 min showed a highly positive correlation with the amount of epinephrine added to the local anesthetic in groups II, III, and IV. In group V the plasma epinephrine concentration showed a marked increase as compared to the baseline level. Plasma norepinephrine concentrations were found to be significantly elevated at 15 and 20 min in group V. A decrease in systolic blood pressure was observed at 4 and 5 min in group II. A decrease in diastolic blood pressure was observed at 5 min in group II; at 3, 4, and 5 min in group IV; and at 2, 3, 4, and 5 min in group V. Heart rate revealed no significant differences from baseline level in any of the groups and there were no significant differences among the groups. It is suggested that exogenous epinephrine added to a local anesthetic may stimulate the presynaptic beta2 receptors on sympathetic nerve endings and on the adrenomedulla, and accelerate the release of endogenous epinephrine.

Adrenal Medulla↗

PubMed2004

A study on attenuation correction using Tc-99m external TCT source in Tc-99m GSA liver SPECT.

PURPOSE: In attenuation correction of ECT images by transmission CT (TCT) with an external 99mTc gamma-ray source, simultaneous TCT/ECT data acquisition is difficult, when the same radionuclide such as 99mTc-tetrofosmin or 99mTc-GSA is used as the tracer. In this case, TCT is usually acquired before administration of the tracer, and ECT is acquired separately after the tracer injection. However, misregistration may occur between the TCT and ECT images, and the repetition of examinations add to the mental and physical stress of the patients. In this study, to eliminate this problem, we evaluated whether attenuation correction of ECT images can be achieved by acquiring TCT and ECT simultaneously, then acquiring ECT alone, and preparing an attenuation map by subtracting the latter from the former using 99mTc-GSA liver ECT. METHOD: The ECT system used was a three-head gamma camera equipped with one cardiac fan beam collimator and two parallel beam collimators. External gamma-ray source for TCT of 99mTc was 740 MBq, and ECT of 99mTc-GSA was 185 MBq. First, pure TCT data were acquired for the original TCT-map, then, ECT/TCT data were acquired for the subtracted TCT-map, and finally, pure ECT data were acquired. The subtracted attenuation map was produced by subtracting the pure ECT image from the TCT/ECT image, and attenuation correction of the ECT image was done using both this subtracted TCT map and attenuation map from pure TCT. These two attenuation corrected images and non-corrected images were compared. Hot rods phantom, a liver phantom with a defect, and 10 patients were evaluated. RESULTS: Attenuation corrected ECT values using the subtraction attenuation map showed an error of about 5% underestimation compared with ECT values of the images corrected by original attenuation map at the defect in the liver phantom. A good correlation of y = 22.65 + 1.06x, r = 0.958 was observed also in clinical evaluation. CONCLUSION: By means of the method proposed in this study, it is possible to perform simultaneous TCT/ECT data acquisition for attenuation correction using Tc-99m external source in Tc-99m GSA liver SPECT. Moreover, it is thought that this method decreases the mental and physical stress of the patients.

Algorithms↗

PubMed2004

Segmented attenuation correction for myocardial SPECT.

PURPOSE: One of the main factors contributing to the accuracy of attenuation correction for SPECT imaging using transmission computed tomography (TCT) with an external gamma-ray source is the radionuclide count. To reduce deterioration of TCT images due to inadequate radionuclide counts, a correction method, segmented attenuation correction (SAC), in which TCT data are transformed into several components (segments) such as water, lungs and spine, providing a satisfactory attenuation correction map with less counts, has been developed. The purpose of this study was to examine the usefulness of SAC for myocardial SPECT with attenuation correction. METHODS: A myocardial phantom filled with Tc-99m was scanned with a triple headed SPECT system, equipped with one cardiac fan beam collimator for TCT and two parallel hole collimators for ECT. As an external gamma-ray source for TCT, 740 MBq of Tc-99m was also used. Since Tc-99m was also used for ECT, the TCT and ECT data were acquired separately. To make radionuclide counts, the TCT data were acquired in the sequential repetition mode, in which a 3-min-rotation was repeated 7 times followed by a 10-min-rotation 4 times (a total of 61 minutes). The TCT data were reconstructed by adding some of these rotations to make TCT maps with various radionuclide counts. Three types of SAC were used: (a) 1-segment SAC in which the body structure was regarded as water, (b) 2-segment SAC, in which the body structure was regarded as water and lungs, and (c) 3-segment SAC, in which the body structure was regarded as water, lungs and spine. We compared corrected images obtained with non-segmentation methods, and with 1- to 3-segment SACs. We also investigated the influence of radionuclide counts of TCT (3, 6, 9, 12, 15, 18, 21, 31, 41, 51, 61 min acquisition) on the accuracy of the attenuation correction. RESULTS: Either 1-segment or 2-segment SAC was sufficient to correct the attenuation. When non-segmentation TCT attenuation methods were used, rotations of at least 31 minutes were required to obtain sufficiently large counts for TCT. When the 3-segment SAC was used, the minimal acquisition time for a satisfactory TCT map was 7 min. CONCLUSION: The 3-segment SAC was effective for attenuation correction, requiring fewer counts (about 1/5 of the value for non-segmentation TCT), or less radiation for TCT.

Adult↗

PubMed2004

Truncation correction of fan beam transmission data for attenuation correction using parallel beam emission data on a 3-detector SPECT system.

BACKGROUND: When the simultaneous transmission computed tomography (TCT)/single photon emission CT (SPECT) acquisition protocol is applied to myocardial studies using a 3-detector SPECT, the narrow effective field of view of a fan beam collimator used for TCT acquisition may cause truncation artifacts on TCT images. In this paper, we propose a new method of correcting for the truncation of TCT. METHODS: The truncated parts of the TCT projection data are corrected using quadratic functions, based on the properties that the integral of non-truncated TCT projection data is constant at any projection angle and the position of the centre of gravity is focused on a fixed point. The usefulness of our method was investigated in phantom and human studies using a 3-detector SPECT equipped with one cardiac fan beam collimator for TCT and two parallel beam collimators for SPECT. We used Tl as a tracer for SPECT and Tc as an external source for TCT. RESULTS: The phantom and human studies showed that our method can adequately correct for the truncation of TCT data acquired using a fan beam collimator in a 3-detector SPECT, as long as there is no truncation in SPECT data. CONCLUSION: Our method appears to be useful for improving the SPECT images obtained using simultaneous TCT/SPECT acquisition in a 3-detector SPECT. However, further studies will be necessary to establish the clinical usefulness of this method.

Algorithms↗

PubMed2003

Evaluation of the number of SPECT projections in the ordered subsets-expectation maximization image reconstruction method.

Filtered back projection (FBP) method, maximum likelihood-expectation maximization(ML-EM) method, and ordered subsets-expectation maximization (OS-EM) method are currently used for reconstruction of SPECT images in clinical studies. In the ML-EM method, images of good quality can be reconstructed even with a small sampling number of projection data, when compared with FBP. Shorter acquisition time and less radionuclide dose are preferable in the clinical setting if image quality is the same. In this study, we attempted to find optimal conditions for reconstruction of OS-EM images with commonly used sampling numbers of 30, 60 and 120 (step angles: 12 degrees, 6 degrees, and 3 degrees, respectively), with acquisition counts/projection of 30, 60, 120 and 240 each. We adjusted the pixel counts of reconstructed images to be constant, by setting combination of sampling number and counts/projection (120 sampling number for 30 counts/projection, 60 for 60, and 30 for 120). Among the 3 acquisition conditions, the small sampling number of 30 had large acquisition counts per direction, resulting in low signal to noise ratio. Under this condition, the resolution was slightly low, but the uniformity of images was high. The combination of OS-EM and smaller sampling projection number may be clinically useful with reduction of the examination time, which is also beneficial to reduce dead time for gamma-camera rotation.

Adult↗

PubMed2002

SPECT imaging with off-set detector system: comparison of sampling angles 2, 4 and 6 degrees.

PURPOSE: We evaluated an off set reconstruction method for single photon emission computed tomography (SPECT), and compared it with the conventional on set reconstruction method, using sampling angles of 2, 4, and 6 degrees. METHOD: A triple-detector system was used. In the off-set acquisition, sampling angles of the opposite detector were shifted 1/2 of the sampling angles of 2, 4, and 6 degrees. For example, when projection data were acquired every 6-degrees (sampling angle = 6 degrees), the projection angles were at 0 degrees, 6 degrees, 12 degrees, and 174 degrees with one detector, and 177 degrees, 183 degrees, 189 degrees, and 357 degrees with the other, opposite, detector. The conventional on set reconstruction images were compared with an off set reconstruction for a pool phantom of uniform concentration, a hot rods phantom, a myocardial phantom, and a human study. RESULTS: The off set reconstruction method was better at all three sampling angles. FWHM (mm) were 11.02 at off-set versus 11.17 at on-set (sampling angle 2 degrees), 11.13 at off-set versus 11.48 at on-set (sampling angle 4 degrees), and 11.24 at off-set versus 11.64 at on-set (sampling angle 6 degrees), respectively. In human myocardium SPECT, visualization of the interventricular septum and cardiac cavity was improved. CONCLUSION: Off set reconstruction by means of filtered back projection will be an efficient sampling mode, having a larger number of effective projection angles.

Adult↗

PubMed2002

Attenuation correction of myocardial SPECT images with X-ray CT: effects of registration errors between X-ray CT and SPECT.

PURPOSE: Attenuation correction with an X-ray CT image is a new method to correct attenuation on SPECT imaging, but the effect of the registration errors between CT and SPECT images is unclear. In this study, we investigated the effects of the registration errors on myocardial SPECT, analyzing data from a phantom and a human volunteer. METHODS: Registerion (fusion) of the X-ray CT and SPECT images was done with standard packaged software in three dimensional fashion, by using linked transaxial, coronal and sagittal images. In the phantom study, an X-ray CT image was shifted 1 to 3 pixels on the x, y and z axes, and rotated 6 degrees clockwise. Attenuation correction maps generated from each misaligned X-ray CT image were used to reconstruct misaligned SPECT images of the phantom filled with 201Tl. In a human volunteer, X-ray CT was acquired in different conditions (during inspiration vs. expiration). CT values were transferred to an attenuation constant by using straight lines; an attenuation constant of 0/cm in the air (CT value = -1,000 HU) and that of 0.150/cm in water (CT value = 0 HU). For comparison, attenuation correction with transmission CT (TCT) data and an external gamma-ray source (99mTc) was also applied to reconstruct SPECT images. RESULTS: Simulated breast attenuation with a breast attachment, and inferior wall attenuation were properly corrected by means of the attenuation correction map generated from X-ray CT. As pixel shift increased, deviation of the SPECT images increased in misaligned images in the phantom study. In the human study, SPECT images were affected by the scan conditions of the X-ray CT. CONCLUSION: Attenuation correction of myocardial SPECT with an X-ray CT image is a simple and potentially beneficial method for clinical use, but accurate registration of the X-ray CT to SPECT image is essential for satisfactory attenuation correction.

Artifacts↗